Sound reproducing apparatus



July 16. 1940 L. BEWAN SOUND RERGDUCING APPARATUS original Filed Jan. '25, 19:55

FIC-3.3.

INVENTOR. Leon Dewan ATTORNEY.

Patented `uly 16, 1940 PATENT yOFFICE SOUND REPRODUCING ArPARATUs Leon Dewan, New York,

per cent to George H.

N. Y., assignor of fifty Callaghan, New York,

` Original application January 26, 1935, Serial No. 3,635', now Patent No. 2,165,236, dated July 11, 1939. Divided and this application August 19,

1938, Serial No. 225,689

7 Claims.

This application is a division' of the application led January 26, 1935,*Serial No. 3,635, now

Patent No. 2-,165,236,of July 11', 1939.

This invention relates to improvements in l sound reproducing apparatus, one object of the invention being the provision of means coordinated with the present type of photoelectric cell sound reproducing apparatus 'and its amplifying means to be actuated by the sound track control light beam, so that the effect therefrom is fed into the input of the photoelectric cell amplier to produce an effect which tends to and does improve the sound from any particular sound track, and particularly where such track is scratched and/ or dirty.

Another object of this invention is the provision of a device of this character which is readily attached` to sound reproducing apparatus as' an adjunct thereto, and without in any way affecting the present apparatus.

Still another object of this invention is the pro'- vision of an apparatus and a method, whereby are formed| a plurality of superimposed' laterally displaced images of the soundtrack so that the light of the images interfere and thus iron out as it were the irregularities in the sound track due to scratches and/or dirt thereon.

In the accompanying drawing:

Figure 1 is a diagramatic view of a complete sound reproducing apparatus With this invention shown therein. v

Figure 2` is a diagram illustrating the effect produced with the apparatus as shown in Figure 1.

Figures 3 and 4 are diagrams illustrating mirror combinations to produce a like effect to that as shownfin Figure 1. y

Referring to the drawing, the numeral 98 designates generally an exciter lamp used in the sound reproducing apparatus, and its beam is projected through the open mask I 8X, upon the concaved mirror |03, having a central opening, through which the reflected beam upon the 'semi-spherical mirror |04 directs the beam through such opening on to the sound track of the film |02. This combination of concave and convex mirrorsserves the purpose of an objective lens to concentrate a ne light slit onthe sound track. The beam v after being affected by the track. is then passed 50 through an aperture |01 in the second mask |06 and through the lens ||5 on to the photoelectric cell |05. 'This cell is connected to the input of the photoelectric cell amplifier |22, which in turn is connected to the power .amplifier |23.and.to the loud speakers (not shown); This partmay'be of usual construction and similar to that now used in general practice.

In order that a sound track, which in usage becomes scratched and soiled, may be used and the scratch or ground noise to a. great extent eliminated in the final sound reproduction, a part of the light after passing through the sound track portion of the ilm 1s caused to form an image that affects a separate photoelectric cell |20. This latter cell is in the nature of a neutralizing or compensating means which being aiected only by the ground noise and not by the sound in the track will act in such manner that whenk dust spots or scratches are present on the sound track their eifect on the cell |05 will be eliminated without affecting the soundper se.

A mirror B, which is formed in two parts disposed at a small angle relative to each other, is positioned in the path of the light beam after its i passage through the sound track to divert light therefrom and form two images displaced from each or relative to each other on the mask H8, having a slit I9, covered with ground glass. Behind this mask is positioned the photoelectric cell'l20, whose amplifier |2 I', is so coupled through the grid of the rst relayof the amplier |22, that the two photoelectric cells |05 and |20v act similarly or in unison on the amplifier |23, except that the effect of the cell |20 is greater for an equal amount of light excitation by virtue of the amplifier |2|. y

A monochromaticy filter |24 is placed tolter the light beam in advancev ofthe mirror H6, so as to cause lighty of only one color to pass, red for example, so that the two images thus formed may be disposed as illustrated in Figure 2. It is assumed that a variabley density track is being reproduced and the twoA images ||1 of an oblong slit-like portion of the track are projected upon the slit |9. It is also assumed that twospots |25 and |26 have just appeared on .the slit as the sound track moves by; The relative position of the two parts of the mirror H6 is such that not only are the two images I7 displaced fromeach diameter of` the larger spots that usually occur in the soundtrack, but: are also very slightly displaced in a direction at right angles to the other direction, so that fairly broad interference bands are produced, preferably parallel to the slit H9. This slit H9 is made to lie in one of the dark bands where the two beams forming the images l1 totally interfere. Where there are no spots on the sound track the slit ||9 is in darkness, re* gardless of. the light Variations due to recorded lother laterally to an extent equal to the average 4.5

sound since both beams of the images ||1 interfere whether they are strong or weak, since they remain of equal intensity. If the spot appears in the sound track and consequently in the images the two areas formed by the spot |25, due to the displacement of the images will each receive light from the luminous portions of each others image, and sincev light from, only one image is present in each area formed by the spotj there will no longer be interference in these areas and visible light results therein. The result of this, is that whenever a dark spot appears in the sound track, the tendency towards a temporary diminution of the output of the amplifier |23, caused by the dark spot is compensated for by the simultaneous appearance at the photoelectric cell |20 of light caused by this same dark spot.

No sound variations are transmitted from the photoelectric cell |20, due to the fact as before described of equal intensity of the images when the sound track is uniform. Only disuniformity, such as spots, dust, etc., appear luminous through the slit ||9, and cause the photoelectric cell |20 to neutralize the eiect of these irregularities upon the amplifier |23.

If desired, the images ||1 may be enlarged, either by means of having the mirror ||6 be slightly convex, and therefore divergent, or by having a special lens or mirror to produce the images at a longer distance therefrom. An astigmatic or cylindrical mirror or lens may also be introduced in the optical system, in order to greatly enlarge the images in the direction of the width of the slit ||9. More than one slit may be used, each slit being placed where a dark band of the interference pattern falls. If desired, the light from the sound track may reach the photoelectric cell |05 directly, without an image thereof being formed, and means may be employed for diverting a part of the light for the compensating or neutralizing photoelectric cell and forming the enlarged' image required therefor.

In Figure 3 is shown such an arrangement, wherein a lens |27, made in two parts |28 and |20, forms the required image With an interference pattern. The formation of the two images is accomplished by displacement of the two halves of the lens at right angles to the plane of the drawing, and the interference pattern is produced either by separation of the two halves or by having one of the halves slightly thicker than the other, in which case the two halves should be at a slightly unequal distance from the mask l I8, so that the two images produced shall both be perfectly focussed thereon. The lens |21 may be astigmatic in order to produce the broadening effect on the images as already described.

If desired, a concave mirror may be used to produce the same results as lens |27. This is shown in Figure 4 where a concave mirror |30 is composed ofv two halves displaced in two directions. For example, the two halves may be Yat an angle with each other to produce the displacement which causes any spots on the sound track to appear double by means of the image formed by the mirror, and may be at slightly unequal distances from the mask ||8 to. produce the interference pattern. The interference pattern may also be produced in this case by slightly rotating the two halves on an axis passing centrally through the mirror at right angles to the split. In the use of either the mirror |30, the lens |21, or the mirror IIB, vthe images produced .this neutralizing means.

thereby may be displaced laterally without causing any effect on the interference pattern.

This may be done in the case of the mirrors IIS or for example, by providing a suicient distance between the two halves thereof.

Instead of'a lens such -as |211, ora spherical concave mirror to produce the image or images of the sound track upon the screen H8, a cylindrical lens or mirror may be used if desired in such manner that an image of the lsound track is produced on the screen |8 only in the lateral plane while the light in the longitudinal plane is allowed to diverge from the sound track and fall on the screenv ||8. The formation of the two images of the sound track to produce double images of the sound track irregularities laterally displaced may in this case be produced by caus' ing the cylindrical lens or mirror used to be split' with its halves at an angle in the lateral plane or by using a two-part reflector or refractor whose parts are also at a slight angle in the -lateral plane. The rays diverging from the sound track in the longitudinal plane without `being acted upon by the cylindrical lens mentioned may be caused to produce lateral interference bands parallel to the slit in the screen by dividing the beam into two portions and causing an overlapping thereof by means of a two-part plane reflector whose parts are at a slight angle in the longitudinal plane or bymeans of a suitable refractor similarly used. If desired the divergence of the beam from the sound track in the longitudinal planek can be somewhat modified and decreased by means of a -cylindrical lens whose axis is in the lateral plane to cause the light rays to be less divergent longitudinally, and the beam divided into two halves at an angle in the longitudinal plane to produce overlapping areas on the screen H8. One of the halves may be retarded in light speed to an extent of suitable relation to the wave length of light used, to produce the width of interference band desired, by means of a plane transparent medium interposed in the beam path, or by having one-half of the cylindrical lens which modifies the beam in the longitudinal plane be thicker than the other half. It is possible in this feature to produce more than two laterally displaced images of the sound track in order to produce a more uniform effect and take care ofthe various sizes of irregularities.

Where variable area sound track is being reproduced, the images on the slit I9 will vary in length simultaneously in accordance with the sound waves though this would not cause sound variations to affect the cell |20, due to the interference conditions described. ,The slit IIS, and/or any other slits covered by the images are placed in the veryfdarkest portion of the dark bands of the interference pattern. If the images are the result of a straight `narrow analyzing aperture of the sound track,then,

present invention. and its modifications Willbe fully understood and its manifold advantages be fully appreciated, when it can be seen that with a soiled, spottedv or scratched sound track, good sound can be produced, bythe simple addition tothe present sound reproducingy apparatuscf l What is claimed is: l

i 1. The method in reproducing 'sound-on lm consisting in scanning the sound track, simultaneously selectingl ground noise components from the scanned sound track by projecting they sound track in such amanner that sound wave images are decreased in visibility relative to vground noise images in the sound track and photoelectrically translating the scanning of the selected ground noise components, and applying Vsaid selected ground noise components simultaneously with the main sound effects to produce a compensatory action whereby the effect of the originalground noise upon the final sound reproduction is neutralized.

2. The combination with `a sound on film re, producing apparatus including a lm progressing mechanism, an exciter lamp, a photoelectric cell, and an amplifying system controlled by the cell,

of neutralizing means consisting of means for projecting the scanning light passing through the track and for decreasing the visibility of sound Waves relative to the extraneous interference carried by said track, and means for applying the modulations of the extraneous interference selected thereby to the amplifying system whereby the effect of said extraneous interference carfried by the sound track is neutralized and re-y duced in the final reproduction of the sound in the system. l

3. The combination as claimed in claim 2 wherein theneutralizin'gmeans includes an auxiliary photoelectric cell the output of'which is connected to the amplifying system.

4. The `.combination as claimed in claim 2,

wherein `the neutralizing vmeans includes 'a light deecting means disposed in the light beam after it has passed through the sound track of the film, and an auxiliary photoelectric cell the output of .which is connected to the amplifying system and Which is in the path of the light after striking the light deflecting means.

5. The combination as claimed in claim 2,

wherein the neutralizing means'includes a light 6. The combination as claimed in c1aimf2` wherein the neutralizing means includes means for producing light wave interference.

7; The combination as claimed in claim 2 wherein the neutralizing means includes means for producing a plurality of displaced super imposed images of the sound track.

LEON BEWAN. 

